0　Introduction

FAST is an Arecibo-type antenna with 3 outstanding aspects: unique karst depression as the site; active main reector which corrects spherical aberration on the ground to achieve full polarization and wide band without involving complex feed system; and light focus cabin driven by cables and servomechanism plus a parallel robot as secondary adjustable system to carry the most precise parts of receivers[1]. The part of main reector which is illuminated by the feed is continually adjusted to t the paraboloid of revolution in real time when tracking the radio source[2].

The focus cabin that carries feed is driven by six cables to follow the focus movement of active reectors on the spherical focus surface. In the focus cabin, besides star framework, there is a parallel robot called Stewart which consists of an upper and a lower platform connected by six extensible limbs through spherical joints in the two planar platforms. Feeds are placed on the lower platform.

1　Measurement system of feed

The structure of the focus cabin is shown in Fig.1. FAST feed measurement task is to provide real-time feedback data of moving feeds position for the astronomical observation, whose precision requirement is 3mm. FAST feeds measurement system uses total station prism system (TPS). In TPS, multiple prisms are attached on the edge of the moving planar platform in the focus cabin of FAST. Multiple total stations, each of which is mounted on top of a stable pier, chase the movement of the prisms, and the position of prisms is continuously measured, thus the position of the feed is obtained.

Fig.1　Structure of FAST and Feed focus cabin

广西低碳城（镇）发展路径研究 ……………………………………………………………………………… 宋书巧 陈嘉妮（1/42）

1.1　Piers

23 steady piers (JD1-JD23) for measurement are built in the main reector field of FAST, as shown in Fig.2. The piers deformation is less than 1 mm by long term monitoring. These piers are divided into three rings, called inner ring, middle ring and outer ring. The feed measurement system is designed to use several total stations which will be mounted on piers in the middle and outer ring. Three metal plates where total stations are mounted on top of each pier so as for total stations working at the same time.

(a) Distribution map of piers

(b) Distribution map of prisms on Stewart lower platform

Fig.2　Distribution map of piers and prisms

1.2　Measuring instruments

+(z-mean(z))2))

1.3　Targets

Prisms are uniformly fixed on the rim of the lower platform of Stewart in the feed focus cabin where the lower platform of Stewart approximates a circle with radius of 2m. They are facing to the total station when the focus cabin is at the lowest point of spherical focus surface.

2　Benefits of trilateration

Due to the electronic distance measurement which can be interfered by the environment effect, there will be many possible errors in the measurement result[7]. Shown by total stations monitoring experiment results at FAST site, the accuracy of measurement data including horizontal angle, vertical angle and distance is greatly inuenced by surrounding atmospheric disturbance[8]. The distance measurement error brought by atmospheric conditions can be greatly reduced by certain correction methods or formulas[9]. However, there is not any effective model or formula to correct angular measurement error at present. Trilateration is usually used for field measurement[10,11]. It was also applied in GBT (Green Bank Telescope) measurement[12]. Inspired by it, trilateration is proposed to be applied in the FAST feed measurement to solve the problem. Instead of angles, only distance is used in trilateration. Through experiments and calculations, measurement coordinate precision of target is improved remarkably.

3　Trilateration method

3.1　Principleoftrilateration

The position of uncertain points can be got by using trilateration calculation through three other known points[13].

Measurement instrument such as total station is installed on point P; three prisms are xed on point A, B and C. Thus distances between point P and A, B, C can be got by measuring, labeled by l1, l2, l3. Given that the 3D coordinate of point A, B and C is already known, which is [X1, Y1, Z1]T, [X2, Y2, Z2]T and [X3, Y3, Z3]T, 3D coordinate of point P can be obtained by trilateration using Eq.(1).

(1)

3.2　Arrangement of total stations based on trilateration

In feed measurement, total-station prism system (TPS) is used to measure three dimensional coordinate of feed. To determine 3D coordinate based on trilateration, nine total stations are required in minimum. Every three total stations chase the movement of a prism which is attached on the edge of feed focus cabin. The position of the prism is determined from the measured distances based on the principle of trilateration. Therefore 3D coordinate of feed is determined according to three prisms position and feed location on the platform (feed location on the lower platform is already known after factory settings called system parameters).

上文已经论述了未经许可演绎作品可依法取得完整著作权，但依然有学者从“应然”的角度认为，未经许可演绎作品取得了著作权后会有损原作品著作权人的利益，即便授予了著作权也应当从权能上予以限制。这都是因为其并未认识到，著作权在行使方式上，在性质上与物权法具有区别。因此，此处将首先探讨著作权与物权所不同的一个特有性质，然后依据该性质来对著作权的行使方式进行分析，最后对部分学者所表现出的担忧予以回应。

In ATR mode total station can provide 0.6mm+1ppm enhanced measurement accuracy to prism. There is a restriction for the position of total stations[14,15]. Following this restriction, analysis of measurement accuracy for feed moving on the spherical focus surface is studied as follows under different arrangements of total stations. In the calculation, prisms #1, #3, #5 are chosen as targets, feed is on the center of the lower platform. The accuracy of feed position on the spherical focus surface in the following arrangements is shown in Fig.3.

Fig.3　Accuracy of feed position in 4 arrangements

3.2.1　Arrangement 1

Every three piers are chosen which are evenly distributed around the prism to the greatest extent. Therefore, in total nine piers are chosen. Three total stations are mounted on three piers which are JD6, JD17 and JD21 to chase prism #1. Similarly, JD8, JD13, JD21 are chosen to chase prism #3, JD10, JD13 and JD17 to chase prism #5.

3.2.2　Arrangement 2

For a certain prism, the nearest pier from middle loop and other two nearest piers from outer loop are chosen. Three total stations are mounted on three piers which are JD6, JD12 and JD13 to chase prism #1. Similarly, JD10, JD20 and JD21 are chosen to chase prism #5, JD8, JD16, JD17 are chosen to chase prism #3.

Third, after polar calculation, the accuracy of targets before and after atmospheric correction is shown in Table 1. The average RMS errors after atmospheric correction is 1.24mm, which represents the average typical accuracy of polar measurement.

For a certain prism, the nearest two piers from middle loop and one nearest pier from outer loop are chosen. Three total stations are mounted on three piers which are JD7, JD11 and JD13 to chase prism #1. Similarly, JD7, JD9 and JD17 are chosen to chase prism #3, JD9, JD11, JD21 are chosen to chase prism #5.

3.2.4　Arrangement 4

An experiment is made at the FAST project site in which mean value is used as truth-value. In this experiment, one total station is installed on pier JD10. Six targets are set on other six piers JD1, JD2, JD3, JD20, JD21, JD22 respectively (JD1, JD2 and JD3 are almost of the same height of 10m, JD20, JD21 and JD22 are almost of the same height about 20m) as shown in Fig.4. The total station uses ATR mode to measure the targets circularly and measures each target once for 5 times repeated measurement. The cycle time is about 200s. Horizontal angle, vertical angle and the distance from total station to targets are measured, meanwhile the meteorological parameters is recorded.

For a certain prism, the nearest two piers from middle loop and one nearest pier from outer loop are chosen. For the other two prisms, the nearest one pier is chosen from middle loop and two nearest pier from outer loop. Three total stations are mounted on three piers which are JD7, JD11 and JD13 to chase prism #1. Similarly, JD8, JD16 and JD17 are chosen to chase prism #3, JD10, JD20, JD21 are chosen to chase prism #5.

（2）融资方式单一。根据调查结果发现，大学生创业选择融资方式时最先考虑的是融资成功率。由于大学生缺乏社会经验及较低的信用条件的现状，银行贷款“惜贷”使其门槛高而难，获得天使投资机会的概率又小，因此中国大学生创业者中大部分只能通过亲情融资、合伙融资的方式筹集创业基金。因此，为了提高大学生创业成功的概率，激发大学生创新创业的潜能，大学生应在选择融资渠道上，更加多元化、创新化。

于是作为董海川最出名的两大弟子之一的程廷华就让朝廷鹰犬给缠上了，慈禧还让光绪下旨，让宫宝田去请他师叔。程廷华想都不想就拒绝了宫宝田，说人各有志，不愿为官。

宝宝说：“爸爸妈妈，请你们在帮我挑选东西前，好好查一查有关的安全标准，避免买来有安全隐患的物品，减少对我的伤害。”

3.3　Conclusion for arrangement of total stations

Through the analysis, the precision of location for feed measurement is relevant to the arrangement of total stations. Moreover, the precision is higher when the total stations are more evenly distributed or nearer.

由图5可看出，随着羟肟酸钠用量的不断增加，粗精矿中铜的回收率明显上升，而其中的铜品位则先升高而后下降。综合考虑，确定羟肟酸钠的适宜用量为100 g/t。

4　Experiment and results

长白山的维管植物共计183科638属2853种，分别占中国维管植物科、属、种总数的61.1%、18.7%和9.2%；海棠山的维管植物共计130科472属2504种，分别占中国维管植物科、属、种总数的43.2%、13.8%和8.0%；百花山的维管植物共计130科456属2604种，分别占中国维管植物科、属、种总数的43.2%、13.3%和8.4%。

4.1　Polar calculation

Commonly 3D coordinate can be obtained by the following steps: First, Due to atmosphere interference, the distance between total station and prisms can be corrected by Eq.(2) and Eq.(3).

Fig.4　Distribution for experiment

(2)

[ 1] Nan R. Five hundred meter aperture spherical radio telescope (FAST) [J]. ScienceinChina: SeriesGPhysics, Mechanics & Astronomy, 2006, 49(2):129-148

(3)

Apparently the accuracy of trilateration calculation is related to the accuracy of distances between the three known points and the unknown point. The accuracy is improved after the atmospheric correction for distance shown in Table 2. It is also strongly related to the configuration of the three known points. If the three known points are reasonably distributed, the accuracy can be very satisfying. After atmospheric correction of distance, considering the trilateration for reasonable configuration used, the RMS error is lower than 0.6mm which is not only much lower than polar calculation but also can meet the requirements for the FAST control system. Therefore, confirmed by experiments, trilateration for feed measurement is effective.

植株样品：将田间植株样本剪切成1 cm以下的小段或切碎，在不锈钢盆中充分混匀，用四分法缩分样品，分取2份200 g的样品，分别装入封口样品容器中，粘好标签，贮存于-20 ℃冰柜中保存。

Second, 3D coordinate of prism can be calculated by

(4)

where θ is pitch angle, φ is roll angle.

RMSE=sqrt((x-mean(x))2+(y- mean(y)) 2

As the development of modern geodetic measurement instrument, most of the main tasks can be fullled with these instruments implicitly by their integrated applications[3-5]. The total station has automatic target recognition (ATR) function which can fulll the need of tracking feed focus cabin of FAST. In ATR mode it can provide 0.6mm+1 ppm enhanced measurement accuracy to prism and 1″ angular accuracy[6].

(5)

3.2.3　Arrangement 3

表1列出了滚动轴承实验的工况，所用的197726型轴承轴承节径D为178.8mm，滚子直径d为23.776 mm，滚子个数为20，接触角为10°，由公式(1)计算得出，外圈故障特征频率fo=67.4 Hz，滚子故障特征频率fb=28.3 Hz。

Table 1　Polar measurement results

TargetRawRMSE(mm)CorrectionRMSE(mm)JD11．631．44JD21．521．38JD31．591．39JD201．371．26JD211．230．93JD221．161．04

4.2　Trilateration calculation

Three prisms are chosen as the known points whose average values for 3D coordinates could be obtained by polar measurement to do trilateration calculation. All the calculation is done with the mathematical tool- MATLAB. Distance correction is done by Eq.(2) and Eq.(3) as well. The RMSE of trilateration calculation before and after atmospheric correction is shown in Table 2.

Table 2　Trilateration calculation results

TargetArrangementRawRMSE(mm)CorrectionRMSE(mm)Accuracyimproved(%)JD10JD1，JD2，JD221．921．6315JD10JD1，JD2，JD35．855．584．6JD10JD1，JD3，JD201．621．4411JD10JD1，JD3，JD221．421．1519JD10JD1，JD20，JD220．840．8415JD10JD20，JD21，JD220．930．5738JD10JD1，JD2，JD211．220．5950

5　Conclusion

These are formulas for atmospheric correction where ΔD1 is atmospheric correction(ppm), P is air pressure(mbar), t is air temperature(℃), h is relative humidity(%), α=1/273.5, X=(7.5×t/(237.3+t))+0.7857, R is raw distance between total station and prisms, Rc is distance after correction.

图5为不同搅拌速度制备样品XRD谱图及二硫化钼、三氧化钼XRD标准谱图。从图5中的曲线350 r/min与二硫化钼、三氧化钼XRD标准谱图对比可知，350 r/min样品中金属钼主要赋存状态为二硫化钼，但是掺杂少量的三氧化钼，集中体现在7°附近有1条三氧化钼XRD特征峰；从曲线500 r/min、650 r/min与二硫化钼、三氧化钼XRD标准谱图对比可知，曲线500 r/min、650 r/min与三氧化钼XRD标准谱图相同，证明500 r/min、650 r/min 样品中金属钼赋存状态为三氧化钼。

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[译文1]We define a species as a group of animals that share certaincharacteristics and produce reproductive offspring when they mate.

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由于多媒体的出现，传统教学方法得到了改革，由“填鸭式”教学，逐渐转变为启发式和探索式教学。为此，教师应该利用多媒体，将课堂还给学生，突出学生的主体性，利用计算机的个别辅导、小组辅导、分组辅导等功能可以将个别辅导和整体教学相结合，做到因材施教，充分发挥学生的主观能动性，调动学生的学习积极性。此外，多媒体教学可以了解和掌握小学生的学习进程，依此进行合理的教学任务安排，为学生留有足够的自我学习时间。

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采用美国麦克公司Au-toPoreⅣ9510型全自动压汞仪，将实验样品在110℃条件下真空脱气2h后进行压汞实验，汞的表面张力为485.0mN/m，汞与煤样的接触角为140°，仪器的压力范围为0.1～60000Pa，测量的孔径范围为3.0nm～1000μm。

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[15] Kirchhof N. Optimal placement of multiple sensors for localization applications[C]. In: Proceedings of the International Conference on Indoor Positioning and Indoor Navigation, Montbeliard-Belfort, France, 2013. 1-10

YuanHui, born in 1983. She is pursuing her Ph.D degree in measurement and control of NAOC at present. She received his B.S. and M.S. degrees from Beijing University of Post and Communications in 2006 and 2009 respectively. Her research interests include the design of algorithms for measurement and control systems.